Tiling option for doing multiple areas

[see24]

build in option for supplying an "analysis unit" raster to projectRoads. If supplied, the algorithm projects roads for each unit independently, and knits together the results. This would be for cases where the full graph is too large to hold in memory - so we would give up on storing and returning the graphs. Apply it to all of BC with TSA as the analysis unit to show application to large landscapes.

[see24]

Another idea to allow using larger areas was to have a low resolution raster first and remove areas with no roads built